1. Field of the Invention
This invention relates to processes for removing protein from yeast cells by alkaline extraction.
2. Description of the Prior Art
In the food industry, the most important protein ingredients are egg white, casein, sodium caseinate, dried milk solids, and nonfat dry milk. Their functional properties, such as solubility, whippability, emulsification capacity, gellation, etc., are the primary factors determining their utility in food applications. Unfortunately they are expensive and in short supply, and although soy protein isolate and concentrate have been used as replacements, they have a bitter beany taste which restricts their usage level.
These important protein ingredients can potentially be replaced by yeast materials, especially those processed products having a bland flavor and a reduced nucleic acid content. It is necessary to extract the protein within the cells and efficiently recover the protein isolate. Many processes have been developed for this purpose, including the alkali extraction process, which has been well established in the soy industry and is also widely applied to protein extraction from microbial cells.
The efficiency of the alkali extraction process is generally determined by the combined effect of alkalinity, temperature, and the length of reaction time. However, one is not only interested in the efficiency of the protein recovery, but also in the functional quality of the protein product for use as a protein ingredient, i.e. solubility, whippability, etc. Because biological materials such as yeast cells are complex, variations in the nature of the cells occur depending on their cultural history. A yeast culture grown under a specific set of conditions still contains a heterogeneous population consisting of individual cells which may be grouped into various categories based on age, morphology, composition, etc., and those yeast cultures grown under different sets of conditions will contain heterogenous populations which vary even more from each other as a group. It is believed that such different cells or different populations will react differently to alkaline extraction depending upon the changes in cultural conditions.
Accordingly, it is an object of this invention to improve the efficiency of alkaline protein extractions from yeast cells by changing the cultural conditions under which the physiological state of the cells are conditioned specifically for this purpose. This and other objects will become clear upon further reading of this specification.